1. Field of the Invention
The present invention relates to a cylinder block for a piston type compressor in which plural cylinder bores are provided in the cylinder block and arranged around a rotating shaft, a piston is housed in each cylinder bore, then each of the pistons is reciprocated in the cylinder bore based on the rotation of the rotating shaft, and each piston causes refrigerant gas to be drawn into a compression chamber, which is defined in the cylinder bore and then discharged from the compression chamber.
2. Description of the Related Art
In a piston type compressor of a variable displacement type, as disclosed in Japanese Unexamined Patent Publication,(Kokai) No. 11-193780, a cylinder block that contains cylinder bores that guide pistons is assembled as a part of a housing assembly of the compressor and the housing assembly comprises a pair of housings (a front housing and a rear housing) and a cylinder block. The cylinder block is clamped by the pair of housings so as to constitute a part of an outer wall of the housing assembly. Plural bolts penetrate the front housing and the cylinder block and are screwed into the rear housing. The pair of housings and the cylinder block are assembled and fixed so as to constitute the housing assembly by tightening the bolts.
The cylinder bores housing the pistons in the cylinder block are arranged at approximately equal intervals around the axis of the rotating shaft and the bolts penetrate between the adjacent cylinder bores and are near the outer circumference of the cylinder block. The bolts penetrate through a crank chamber in the front housing and the end surface of a cylindrical circumferential wall of the front housing is coupled with the outer circumferential portion of an end surface of the cylinder block. In this structure, in which the front housing and the cylinder block are coupled to each other, the tightening force of the bolts causes the cylinder block to be deformed slightly and the cylindrical cylinder bores are then deformed. The deformation of the cylindrical cylinder bores prevents the pistons from moving smoothly. Besides, unnecessarily large clearances, between the circumferential surfaces of the pistons and the circumferential surfaces of the cylinder bores, are created, so that the refrigerant compressed in the cylinder bores leaks into the crank chamber through the clearances between the circumferential surfaces of the pistons and the circumferential surfaces of the cylinder bores. The excessive leakage of the refrigerant from the cylinder bores to the crank chamber disturbs the pressure in the crank chamber, which should be regulated, so that the displacement control in the compressor of a variable displacement type becomes unstable.
A piston type compressor in which a cylinder block is included in a housing assembly constituted by coupling a first housing to a second housing is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 10-306773. The structure in which the cylinder block is included in the housing assembly prevents the coupling portions between the first housing and the cylinder block, and the coupling portions between the second housing and the cylinder block, from being exposed on the outside of the compressor. The hiding of the coupling portions is effective for reducing the possibility of leakage of refrigerant from the compressor.
The cylinder block is held, for example, by being interposed between the first housing and the second housing. In the piston type compressor in which the cylinder block is located inside the housings, the diameter of the cylinder block tends to be small. Therefore, in the structure in which the first housing comes into contact with the one end surface of the cylinder block and the second housing comes into contact with the other end surface of the cylinder block and then both of the housings are coupled by tightening bolts, a cylinder block with small diameter is easily deformed.
The object of the present invention is to prevent the cylinder bores in the cylinder block from being deformed.
Therefore, the present invention applies to a piston type compressor in which plural cylinder bores are provided in a cylinder block and arranged around a rotating shaft, a piston is housed in each cylinder bore, then each of the pistons is reciprocated in the cylinder bore based on the rotation of the rotating shaft, and the piston causes refrigerant gas to be drawn into a compression chamber which is defined in the cylinder bore and then discharged from the compression chamber. In the first aspect of the present invention, a deformation absorbing gap that absorbs the deformation of the cylinder block is provided, for at least a pair of the adjacent paired cylinder bores, between the adjacent paired cylinder bores.
The deformation of the cylinder bores due to the deformation of the cylinder block is avoided by the enlargement and the contraction of the deformation absorbing gaps.
The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below, together with the accompanying drawings.